1. Field of the Invention
The present invention relates to a canister for a vehicle. More particularly, the present invention relates to a canister for use with a fuel tank to prevent fuel vapor diffusion into the atmosphere.
2. Related Art
Recently, from the viewpoint of environmental protection, the air, including the fuel vapor, produced when refueling need to be adsorbed by means of an adsorbent within a canister. Such adsorption prevents diffusion of fuel vapor into the atmosphere.
Incidentally, in a conventional canister for a vehicle such as that disclosed in U.S. Pat. No. 4,951,643, to increase the adsorption efficiency of the canister when not refueling, in other words, to decrease the air leakage rate of fuel vapor, extending the adsorbent in the channel or flow direction has been effective. In addition, as the fuel vapor is adsorbed and the amount thereof decreased gradually from the end portion on the fuel tank side of the adsorbent, it has proven effective, concerning both increasing adsorption efficiency and miniaturizing the canister, to design a channel cross-sectional area of the adsorbent into a shape wider at the side of the fuel tank and narrower on the side of the atmosphere. However, if either extending the adsorbent in the channel direction or designing the cross-sectional area of the channel mentioned above is performed in order to decrease the air leakage rate of fuel vapor when not refueling, the channel resistance of the canister is increased.
To prevent fuel vapor diffusion into the atmosphere when refueling, it is necessary to treat a flow rate of air including fuel vapor, thirty liters per minute, for example, by means of the canister. However, because the aforementioned canister, which adsorbs fuel vapor when not refueling (hereinafter referred to as a canister for an evaporator), produces a large resistance for the reason described above, such a large quantity of air including fuel vapor can not be effectively handled. Accordingly, taking R for a channel resistance of the canister and Q for a flow rate of the air including the fuel vapor when refueling (refueling flow rate), a positive pressure, corresponding to a pressure loss in the canister, R.times.Q, is generated in the fuel tank, and if the value of the pressure loss is greater than a predetermined pressure, the autostop of the refueling device operates to make refueling impossible.